This invention relates to a fabricated rotor wheel of sheet metal for radial-flow fans, turbines, and the like, where the sheet metal blades have angled legs for attachment to a suitably configured sheet metal rotor dish.
On a rotor wheel disclosed by German Pat. No. 809,690, the sheet metal blades are attached by welding, and more particularly, the blades have angled legs for attachment by projection welding.
While sheet metal rotor wheels having blades attached to them by conventional welding (above-mentioned German Patent) afford an improvement over earlier constructions where the blades were riveted into place, they nevertheless suffer from the disadvantage that they are not suitable for elevated rotational speeds because conventional welding fails to give them the requisite strength. The reason for this is that fitting the blade legs to the sheet metal dish of the rotor wheel before welding is very difficult and that for lack of time it cannot normally be performed with the necessary high degree of accuracy, so that the weld will lack adequate homogeneity. A further disadvantage of these welded rotor wheels is that conventional welding methods cause excessive distortion of the rotor wheel which is very difficult to eliminate afterwards and thus cause eccentricities which at high rotational speeds produce severe unbalances in the rotor wheel. A still further disadvantage of such welded rotor wheels is that welding contaminates the surfaces in contact with fluid flow in use of the rotor wheel and such contaminated surfaces, which are difficult to eliminate, add to the losses during flow through the rotor wheel.
Conventional welding as in the above-mentioned German Patent further poses practically insurmountable problems when the blades on the wheel are closely spaced together or when the rotor wheels are a small size, because the working space allowed for welding would then be inadequate.
The present invention contemplates providing a rotor wheel for radial-flow fans and turbines which is suitable for use at extremely high rotational speeds and where, accordingly, the joint between the blades and the wheel dish exhibits a maximum of strength. The rotor wheel contemplated by this invention likewise shows a clean surface and a high degree of centricity, these properties being achieved with a small amount of manufacturing effort.
The present invention more particularly contemplates providing a rotor wheel where the sheet metal blades are attached to the rotor dish by means of explosion welding.
An explosion-welded rotor wheel according to the present invention meets the cited requirements with entire satisfaction, giving a high-strength joint, little distortion, and a clean surface while economizing the cost of manufacture. The great strength of the joint is achieved primarily by a 100% contact weld between the bearing surface of the blade legs and the wheel dish. Manufacturing cost is economized by joining all the blades to the wheel dish in a single operation and by producing the joint at the speed of explosion.
In a further aspect of the present invention the sheet metal blades are of T-shaped cross-section formed by joining together two L-shaped blade portions. The advantage afforded by this construction is that it provides the contact surface needed for a sound joint while avoiding the high notch stresses that would be sure to occur in the outer edge of the angled blade stem if use were made of singly bent sheet blades of L-shape.
In a further aspect of this invention the two blade portions are joined together by brazing or spot welding. Sheet blades made in this manner are characterized by economy in manufacture, and they will fully meet the strength requirements since no severe stresses will occur in use in the location where the two blade portions are joined together.
The present invention further contemplates a method of manufacturing a rotor wheel assembled in accordance with the foregoing detailed description, said method being characterized by the following successive operations:
The rotor dish, with a thin layer of explosive applied to its radially inner surface, is then held over the blade legs at a short distance from them. The explosive is finally ignited using suitable means at the smallest internal diameter of the rotor dish. The explosion, its front traveling outward from the point of ignition, joins the dish to the blade legs by an action which compares to rolling under high pressure. In the process the dish is welded to the blade legs.
The prime advantages in this method are the great strength of the weld joint, the rapidity of joining, and ultimately the repeatability of the joining process, where manual operations are eliminated altogether in the welding and assurance is provided that the rotor wheels formed by the method of the present invention are interchangeable inasmuch as the strength of the blade-to-dish joint will not vary from one wheel to the next. Another benefit is that subsequent treatment of the rotor wheel, such as stress relieving or cleaning of the surface, is obviated. Cleaning is required solely on the smooth side of the rotor dish, the one pointing away from the flow and blades.
The present invention further contemplates providing apparatus for implementing the cited method, said apparatus being characterized as follows: Arranged on a horizontal, disc-shaped base plate is an outer, high-strength supporting ring the internal diameter of which is equal to the outer diameter of the rotor wheel. Placed inside the supporting ring is a number of supporting segments which corresponds to the number of blades on the wheel where, in keeping with the shape of the blades, a preferably radially extending gap the width of the thickness of a blade is allowed to remain between adjacent segments. The surface of the supporting segments exhibits the contour of the wheel dish, where depressions are provided in the gap areas which exhibit the contours of the blade legs and the depth of which is equal to the thickness of the blade legs.
The advantage in this apparatus is that it simply but nevertheless adequately supports the sheet blades to be welded to the runner or wheel dish and that the particular configuration of the surface of the supporting segments permits a weld to be achieved which is free from edge gaps and thus shows an excellent surface finish.
Further objects and advantages of the present invention are described more fully in light of the accompanying drawings.